Two independent lines of investigation already initiated in our laboratory will be continued and expanded. These comprise: 1. A study of how spines sprout, form synapses, and in certain cases regress during ontogenesis of neural structures in situ, and 2. A morphological investigation of the organization of "reconstituted" neuronal aggregates formed in vitro, aimed to ascertain the degree of morphological differentiation which reassociated neurons have to attain in order to be able to form and maintain synaptic contacts. Golgi and electronmicroscopic techniques will be primarily used in these investigations. Successful Golgi impregnations of neuronal aggregates "reconstituted" in vitro, similar to those to be used in these studies, have already been obtained in our laboratory.